The present invention relates to a comb type filter having a hybrid IC (integrated circuit) having a ultrasonic wave solid delay line and its related process circuit. In particular, the present invention relates to such a filter which is mounted in a single housing, and the characteristics of the filter are subject to trimming in the production stage.
A comb type filter is used in a television receiver set for separating intensity signal and color signal.
FIG. 3 shows a circuit diagram of a separation circuit of intensity signal and color signal. In the figure, the numeral 1 is a video signal source, 2 is an ultrasonic wave solid delay line, 3 is a process circuit coupled with said delay line 2, C-OUT is an output terminal of color signal, Y-OUT is an output terminal of intensity signal. The process circuit 3 has impedance elements Z.sub.1 through Z.sub.8, variable resistors VR.sub.1 and VR.sub.2. The impedance elements Z.sub.1 and Z.sub.6 are used for providing impedance matching at input and output of the delay line 2. The impedance elements Z.sub.3, Z.sub.7 and Z.sub.8 function to send signal from an input of the delay line 2 to an output of the same. The impedance element Z.sub.2 and the variable resistor VR.sub.2 adjust the level of the signal which is sent from input side to output side.
The variable resistors VR.sub.1 and VR.sub.2 adjust the characteristics of the filter. When the resistance of the variable resistor VR.sub.1 is high, the dip frequency f.sub.a in FIG. 4 shifts to the low frequency, and when that resistance is low, that dip frequency shifts in the opposite direction. Therefore, the variable resistor VR.sub.1 is adjusted so that the dip frequency f.sub.a coincides with the distribution of the color signal. Similarly, the variable resistor VR.sub.2 adjusts the gain (or attenuation) of the comb filter.
Conventionally, an ultrasonic wave delay line 2 and a process circuit 3 in FIG. 3 are produced separately. And, the variable resistors VR.sub.1, VR.sub.2 and some other components which are subject to adjustment are provided as external components, which are attached to the circuit through a soldering process.
Accordingly, a prior comb filter has the disadvantage that the size is large. Further, it has the disadvantage that the adjustment of the variable components is troublesome, since the adjustment is carried out after the comb filter is assembled into a device, like a television receiver set. The adjustment of the comb filter at the production stage is impossible in the structure of a prior comb filter.